Low angle jack planes have long been used in woodworking, and planes having adjustable mouths have also long been used. Adjustability of the mouth (through which the plane blade projects) is desirable because it usually is preferable to use as narrow a mouth as possible for the depth of cut (or thickness of shaving produced), but depth of cut must be adjustable, with the result that the thickness of the shaving produced changes. Thicker shavings require a larger mouth opening. Adjustable mouths can be provided by making the frog to which the plane blade is secured repositionable so that the blade can be differently positioned relative to the leading edge of the mouth in the plane sole. A particularly desirable structure for providing both an adjustable mouth and support for the cutter or blade is disclosed in U.S. Pat. No. 6,615,497 for a Bench Plane, which is incorporated herein by reference. However, production of a plane with an extremely low bed angle makes it difficult to use movable frog structures.
Adjustable mouths have long been achieved in low angle planes by providing an adjustable toe ahead of the plane blade. Such a toe has a bottom coplanar with the plane body sole and can slide forward and backward to make the mouth opening ahead of the blade smaller or larger. Such a toe is usually secured to the plane body by rotating the front knob on the plane around a threaded stud that projects from the toe through a hole in the plane body until the knob (acting as a “nut” on the threaded stud) contacts the plane body, thereby securing the toe to the underside of the plane body.
One drawback associated with use of an adjustable toe is that the toe can slide backward, for instance, if it strikes a protrusion from the work-piece or a benchstop, and contact and damage the cutting edge of the plane blade. It can also be difficult to adjust the position of the toe by the small increments often necessary in order to position the toe precisely where desired to achieve a particular mouth opening ahead of the plane blade.
Another difficulty associated with adjustable mouth planes is that smaller mouth openings create a greater tendency for the mouth to become clogged with shavings, which requires interruption of use of the plane in order to clear the mouth.